The optical instruments of satellites that have at least one mirror have to be protected against the direct solar inputs on the surfaces of this mirror. The protection measures avoid optical disturbances and make it possible to regulate the temperature in proximity to the focal planes. This protection ensures the optical efficiency of the instruments.
These instruments are mounted on satellites that are placed in orbit by launch vehicles. Because of the small volume allotted under the nose cone of the launch vehicle, it is not possible to have a fixed protection device arranged in front of the optical instrument. It is therefore necessary to deploy this protection in flight, before the operational phase.
The technical problems encountered in the case of the deployment of large structures are primarily:
In the stored configuration: restricted volume for storing the structure, maintaining the integrity of this structure in the folded-down configuration, despite the mechanical and thermal stresses due to the launching of the space craft (notably the non-degradation of the very fragile thermal protection elements).
During deployment: the control of the deployment in terms of kinematics and the regulation of the speed in order to avoid shocks at the end of deployment.
In the deployed configuration: ensuring the stability and the rigidity in flight in order to guarantee the steerability of the craft, and ensuring a correct positioning of the structure in order to ensure that the solar input is limited and the field of view is not blocked.
FIG. 1 represents a device for protecting an optical instrument of a satellite according to the prior art. This device comprises a planar solar screen 101 positioned at a certain distance from the satellite 100. To use a planar screen it is necessary, in certain missions, to have a rotating element (the solar screen) of large size. This solution also poses problems: of reliability, of AOCS (Attitude Orbit Control System) disturbance, of disturbances in the optical measurements and of life span due to the mechanical elements implemented.
Furthermore, in order to avoid the solar inputs during certain periods, additional swivels of the solar screen are necessary, which further increases the complexity of this type of solution.
Thus, a close protection of the beam or beams is a solution that is more effective because it does not involve any movement throughout the operational phase.
To produce this type of jacketing protection, it is possible to use a number of technologies based on a deployable bearer structure for holding and positioning a flexible substrate.
The bearer structure may be inflatable and able to be made rigid in flight but controlling the deployment is complex because it is difficult to model by computation and complex to test. Furthermore, the rigidifying methods are irreversible and therefore do not allow for a model intended for flight to be tested on the ground.
Flexible protection devices are already known that are based on the use of a sheath of flexible cylindrical form, consisting of thermal protection sheets. This element is folded on itself during the stored phase then deployed and powered up. This solution presents a number of drawbacks. First of all, in storage, it is difficult to avoid the degradation of the membranes that form the thermal protection fabric. They are very fragile and are sensitive to mechanical stresses. The degraded membrane produces particles which, in deployment, are dispersed onto the instrument and degrade the optical efficiency thereof. Furthermore, to obtain compact storage, the flexible elements have to be folded and this folding is generally irreversible and has an embrittling effect on the membrane. Finally, the quantity of elements to be deployed, of moving parts and of frictions between components makes the deployment difficult to calculate and difficult to reproduce. The result of this is an overestimation of the energy needed when powering up the flexible element, in order to ensure a good final positioning for it, which can result in degradations on certain components and on the membrane.